Donor‐Flexible Bis(pyridylidene amide) Ligands for Highly Efficient Ruthenium‐Catalyzed Olefin Oxidation

An exceptionally efficient ruthenium‐based catalyst for olefin oxidation has been designed by exploiting N,N′‐bis(pyridylidene)oxalamide (bisPYA) as a donor‐flexible ligand. The dynamic donor ability of the bisPYA ligand, imparted by variable zwitterionic and neutral resonance structure contributions, paired with the redox activity of ruthenium provided catalytic activity for Lemieux–Johnson‐type oxidative cleavage of olefins to efficiently prepare ketones and aldehydes. The ruthenium bisPYA complex significantly outperforms state‐of‐the‐art systems and displays extraordinary catalytic activity in this oxidation, reaching turnover frequencies of 650 000 h^?1 and turnover numbers of several millions.     

Preparation of nano‐chitosan Schiff‐base copper complexes and their anticancer activity

A new kind of nano‐chitosan Schiff‐base Cu complexes with particle sizes of 350 nm were prepared by combination of nano‐chitosan, Cu and Schiff‐base, and characterized by FT‐IR spectra, TEM, DLS and elemental analysis. The modes and mechanism of interaction of the copper complexes with DNA were studied by the fluorescent probe method and electrophoresis analysis. The results suggest that the Cu complexes bound to DNA by electrostatic and intercalation modes. The anticancer activity of the Cu complexes was evaluated by Sulforhodamine B (SRB) assay in vitro. Nano‐chitosan and their Schiff‐base Cu complexes inhibited the growth of the liver cancer cell lines SMMC‐7721 in vitro. The inhibition rate of Schiff‐base Cu complexes was higher than that of nano‐chitosan. Nano‐chitosan combining with Schiff‐base and Cu improved their anticancer activity, which ascribed to the synergistic effect between the chitosan matrix and the planar construction of the Cu complexes. Copyright © 2008 John Wiley & Sons, Ltd.     

Selective Reduction of CO2 to a Formate Equivalent with Heterobimetallic Gold‐ ‐ ‐Copper Hydride Complexes

A series of heterobimetallic complexes containing three‐center, two‐electron Au−H−Cu bonds have been prepared from addition of a parent gold hydride to a bent d¹⁰ copper(I) fragment. These highly unusual heterobimetallic complexes represent a missing link in the widely investigated series of neutral and cationic coinage metal hydride complexes containing Cu−H−Cu and M−H−M⁺ moieties (M=Cu, Ag). The well‐defined heterobimetallic hydride complexes act as precatalysts for the conversion of CO₂ into HCO₂Bpin with HBpin as the reductant. The selectivity of the heterobimetallic complexes for the catalytic production of a formate equivalent surpasses that of the parent monomeric Group 11 complexes.     

Gas‐phase doubly charged complexes of cyclic peptides with copper in +1, +2 and +3 formal oxidation states: formation,structures and electron capture dissociation

Copper complexes with a cyclic D‐His‐β‐Ala‐L‐His‐L‐Lys and all‐L‐His‐β‐Ala‐His‐Lys peptides were generated by electrospray which were doubly charged ions that had different formal oxidation states of Cu(I), Cu(II) and Cu(III) and different protonation states of the peptide ligands. Electron capture dissociation showed no substantial differences between the D‐His and L‐His complexes. All complexes underwent peptide cross‐ring cleavages upon electron capture. The modes of ring cleavage depended on the formal oxidation state of the Cu ion and peptide protonation. Density functional theory (DFT) calculations, using the B3LYP with an effective core potential at Cu and M06‐2X functionals, identified several precursor ion structures in which the Cu ion was threecoordinated to pentacoordinated by the His and Lys side‐chain groups and the peptide amide or enolimine groups. The electronic structure of the formally Cu(III) complexes pointed to an effective Cu(I) oxidation state with the other charge residing in the peptide ligand. The relative energies of isomeric complexes of the [Cu(c‐HAHK + H)]²⁺ and [Cu(c‐HAHK ? H)]²⁺ type with closed electronic shells followed similar orders when treated by the B3LYP and M06‐2X functionals. Large differences between relative energies calculated by these methods were obtained for open‐shell complexes of the [Cu(c‐HAHK)]²⁺ type. Charge reduction resulted in lowering the coordination numbers for some Cu complexes that depended on the singlet or triplet spin state being formed. For [Cu(c‐HAHK ? H)]²⁺ complexes, solution H/D exchange involved only the N–H protons, resulting in the exchange of up to seven protons, as established by ultra‐high mass resolution measurements. Contrasting the experiments, DFT calculations found the lowest energy structures for the gas‐phase ions that were deprotonated at the peptide C_α positions. Copyright © 2012 John Wiley & Sons, Ltd.     

In vitro cytotoxic and apoptotic effect of vic‐dioxime ligand and its metal complexes

In this study, vic‐dioxime ligand, (1E,2E)‐2‐(hydroxyimino)‐N′‐[(1E)‐2‐oxo‐2‐phenylethylidene]ethanehydroximohydrazide (LH₂), and its Cu (II) and Ni (II) transition metal complexes were synthesized and characterized using analytical and spectroscopic techniques. Furthermore, in vitro cytotoxic and apoptotic effects of this vic‐dioxime ligand and its Cu (II) and Ni (II) complexes on Caco‐2 heterogeneous human epithelial colorectal adenocarcinoma cells were evaluated. The effect of the vic‐dioxime ligand and its Ni (II) and Cu (II) complexes in combination with Campto on the cells was also investigated. The cytotoxicity test was carried using the MTT assay, and the apoptotic effect was tested by DNA diffusion assay. Campto was used as a standard anti‐cancer drug, Caco‐2 cancer cells treated with dimethylsulfoxide acted as solvent control, and human peripheral lymphocytes were used as control. The ligand and its complexes exhibit concentration‐dependent cytotoxic and apoptotic behavior. The ligand induces the weakest cytotoxic and apoptotic effects on both Caco‐2 cancer cells and lymphocytes. The Ni (II) complex of ligand induces high cytotoxic and apoptotic effects on both Caco‐2 cancer cells and lymphocytes. The Cu (II) complex of ligand has high cytotoxic and apoptotic effects on Caco‐2, but weak cytotoxic and apoptotic effects on lymphocytes. The cytotoxic and apoptotic effects of the ligand and its Ni (II) and Cu (II) complexes were found to be concentration dependent, i.e. the higher the concentration is the more cytotoxic it will be. The present findings suggest that Cu (II) complex has the potential to act as a promising anti‐cancer compound against Caco‐2 colon cancer cells.     

Effect of coordination sphere of the copper center and Cu―Cu distance on catechol oxidase and nuclease activities of the copper complexes

To explore the effect of Cu―Cu distance in the structure of copper complexes on their catechol oxidase and nuclease activity, six copper complexes with a similar coordination sphere but different Cu―Cu distances were synthesized and characterized with elemental analysis, single‐crystal X‐ray diffraction, molar conductivity measurements, IR and UV–visible spectroscopy. Complex 1 is a binuclear copper complex and complex 4 is a polynuclear complex with a Z‐chain structure, as evidenced by their crystal structures. Complementary characterizations showed that complexes 2 and 3 have a similar binuclear structure to the complex 1 ; and complexes 5 and 6 are analogous to complex 4 . The catechol oxidase activity of complexes 1 , 2 , 3 is quite akin to that of 4 , 5 , 6 , suggesting that the catechol oxidase activity of the complexes was determined by the coordination environment of the copper center, when Cu―Cu distance is large. In contrast, DNA cleavage activity of the complexes 1 , 2 and 3 are much higher than that of 4 , 5 and 6 , indicating that the planar ligand structure in the complexes 4 , 5 and 6 is more critical than the copper coordination sphere and the Cu―Cu distance for their nuclease activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and spectroscopic characterizations of Cu(II) complexes with novel 15‐membered N4 macrocyclic ligand and their utility to obtain CuO nanostructures for efficient degradation of dyes

This paper describes synthesis, characterization and application of a series of Cu(II) complexes with a novel 3‐thioxo‐[1,2,4,5]tetrazocane‐6,8‐dione (N₄) macrocyclic ligand. The complexes were characterized by physicochemical and spectroscopic techniques, such as UV–visible and IR spectroscopies, molar conductance, magnetic susceptibility measurements, and elemental analysis. The data suggest that the mononuclear Cu(II) complexes have a metal‐to‐ligand mole ratio of 1:1 and that the Cu(II) ions are coordinated with the four nitrogen atoms inside the N₄ macrocyclic ring. The experimental anisotropic g‐values indicate that the chloro, nitrato, acetate, and perchlorato complexes have six‐coordinate distorted octahedral behavior, whereas the sulfato complex has five‐coordinate square‐pyramidal geometry. A simple and nontoxic method for preparation of CuO nanoparticles based upon the thermal decomposition of the synthesized Cu(II) complexes has been explored. Finally, the degradation of Rhodamine 6G dye by the catalytic performance of nano‐sized CuO material has been evaluated.     

Reactivity Studies of Iridium Pyridylidenes [TpMe2Ir(C6H5)2(C(CH)3C(R)NH] (R=H,Me, Ph)

The reactivity of a series of iridium? pyridylidene complexes with the formula [Tp^Me2Ir(C₆H₅)₂(C(CH)₃C(R)N H] ( 1 a – 1 c ) towards a variety of substrates, from small molecules, such as H₂, O₂, carbon oxides, and formaldehyde, to alkenes and alkynes, is described. Most of the observed reactivity is best explained by invoking 16 e^? unsaturated [Tp^Me2Ir(phenyl)(pyridyl)] intermediates, which behave as internal frustrated Lewis pairs (FLPs). H₂ is heterolytically split to give hydride? pyridylidene complexes, whilst CO, CO₂, and H₂C?O provide carbonyl, carbonate, and alkoxide species, respectively. Ethylene and propene form five‐membered metallacycles with an IrCH₂CH(R)N (R=H, Me) motif, whereas, in contrast, acetylene affords four‐membered iridacycles with the IrC(?CH₂)N moiety. C₆H₅(C?O)H and C₆H₅C?CH react with formation of Ir? C₆H₅ and Ir? C?CPh bonds and the concomitant elimination of a molecule of pyridine and benzene, respectively. Finally the reactivity of compounds 1 a – 1 c against O₂ is described. Density functional theory calculations that provide theoretical support for these experimental observations are also reported.     

2,5‐Bis(2‐(diphenylphosphino)phenyl)‐1,3,4‐oxadiazole ligands and their Cu(I) complexes for Sonogashira coupling reaction

Two diphosphane ligands – 2,5‐bis(2‐(diphenylphosphino)‐5‐R)phenyl)‐1,3,4‐oxadiazole ( L1 , R = H, L2 , R = OMe) and their binuclear complexes, L1Cu and L2Cu , were prepared and characterized. The molecular structures of L1Cu and L2Cu , as perchlorate salts, were established by X‐ray crystallography, which showed them to be binuclear complexes with each Cu atom tetrahedrally coordinated by two P atoms and two N atoms. The ligands and their Cu(I) complexes catalyzed Sonogashira coupling reactions of iodobenzene with phenylacetylene in the presence of K₂CO₃ under Pd‐free conditions. Coupling reactions catalyzed by L1 or L2 with Cu(MeCN)₄ClO₄ in situ exhibited better yields than those by the corresponding Cu(I) complexes L1Cu or L2Cu . Detailed studies showed L1 or L2 with Cu(MeCN)₄ClO₄ to be suitable catalysts for the coupling reaction of terminal alkynes and aryl halides. The coupling reactions of aryl iodides with electron‐withdrawing groups showed better results. Copyright © 2014 John Wiley & Sons, Ltd.     

Pyridylidene‐Mediated Dihydrogen Activation Coupled with Catalytic Imine Reduction

In recent years, dihydrogen activation at non‐metallic centers has received increasing attention. A system in which dihydrogen is trapped by a pyridylidene intermediate that is generated from a pyridinium salt and a base is now reported. The dihydropyridine formed in this process can act as reducing agent towards organic electrophiles. By coupling the hydrogen‐activation step with subsequent hydride transfer from the dihydropyridine to an imine, a catalytic process was established. Treatment of the N‐phenylimine of phenyl trifluoromethyl ketone with 5–20 mol % of N‐mesityl‐3,5‐bis(2,6‐dimethylphenyl)pyridinium triflate and 0.3–1.0 equivalents of LiN(SiMe₃)₂ under 50 bar of hydrogen gas resulted in high conversion into the corresponding amine.     

Electrochemical Study of Tryptophan‐containing Peptides‐Cu(II) Complexes

This article presents rotating ring‐disc electrode investigations of (A = alanine, F = phenylalanine, G = glycine, L = leucine, W = tryptophan) W, GW, WGG, GWG, GGW, GWGG, and GGWA. In addition, the analyses of the copper complexes of the same peptides plus GF, FGG, GFG, FGG, GGFL, GGGG, AAAA, and GGGGGG have been carried out. The results suggest that an influential step in the reaction mechanism of the copper complexes of the tryptophan‐containing peptides (W‐peptides) is the alteration of the peptide structure after the one‐electron oxidation of tryptophan. This change in structure leads to a positive shift in redox potential for the Cu(III)/Cu(II) couple. The analytical implications for the electrochemical detection of W‐peptides as their copper complexes are applied for detection of W‐containing bioactive peptides. Application of the optimized detection conditions of peptides as their Cu(II) complexes are as follows: (1) If sensitivity is paramount, detect the copper complexes at a relatively high potential, around 0.7 V vs. Ag/AgCl. (2) If selectivity is paramount, use a dual electrode detector, oxidize at an upstream anode at 0.4 V, and detect at the downstream cathode at 0–0.1 V.     

New Transition and Actinide Metal Complexes of 2‐Carboxy‐phenylhydrazo‐Benzoylacetone Ligand: Synthesis,Characterization and Biological Study

A new series of binary mononuclear complexes were prepared from the reaction of the hydrazone ligand, 2-carboxyphenylhydrazo-benzoylacetone (H2L), with the metal ions, Cd(II), Cu(II), Ni(II), Co(II), Th(IV) and UO2(VI). The binary Cu(II) complex of H2L was reacted with the ligands 1,10-phenanthroline or 2-aminopyridine to form mixed-ligand complexes. The binary complexes of Cu(II) and Ni(II) are suggested to have octahedral configurations. The Cd(II) and Co(II) complexes are suggested to have tetrahedral and/or square-planar geometries, respectively. The Th(IV) and UO2(VI) complexes are suggested to have octahedral and dodecahedral geometries, respectively. The mixed-ligand complexes have octahedral configurations. The structures of all complexes and the corresponding thermal products were elucidated by elemental analyses, conductance, IR and electronic absorption spectra, magnetic moments, 1H NMR and TG-DSC measurements as well as by mass spectroscopy. The ligand and some of the metal complexes were found to activate the enzyme pectinlyase.     

Synthesis and spectroscopic characterization of transition metal complexes derived from novel benzofuran hydrazone chelating ligand: DNA cleavage studies and antimicrobial activity with special emphasis on antituberculosis

Mononuclear divalent complexes of Co, Ni, Cu and Zn derived from a benzofuran‐based novel hydrazone tridentate ligand were synthesized and characterized using various spectroscopic methods. Elemental analysis reveals that the metal‐to‐ligand ratio is 1:2 which is supported by mass spectrometry results. Conductivity measurements suggest that all the complexes are non‐electrolytic in nature. The ligand and complexes were evaluated for their antimicrobial potency. Bioassay of all hydrazone chelates shows enhanced activity as compared to that of the ligand. The complex with cobalt ion as the metal centre shows better activity against fungi than the standard. Also, ligand and complexes were screened for antituberculosis activity; some analogues (Ni, Cu, Zn) are eight times more active than the standard. Both ligand and complexes show moderate ability to cleave calf thymus DNA. Copyright © 2015 John Wiley & Sons, Ltd.     

Polymer‐anchored mononuclear and binuclear CuII Schiff‐base complexes: Impact of heterogenization on liquid phase catalytic oxidation of a series of alkenes

Liquid phase catalytic oxidation of a number of alkenes, for example, cyclohexene, cis‐cyclooctene, styrene, 1‐methyl cyclohexene and 1‐hexene, was performed using polymer‐anchored copper (II) complexes PS‐[Cu (sal‐sch)Cl] ( 5 ), PS‐[Cu (sal‐tch)Cl] ( 6 ), PS‐[CH₂{Cu (sal‐sch)Cl}₂] ( 7 ) and PS‐[CH₂{Cu (sal‐tch)Cl}₂] ( 8 ). Neat complexes [Cu (sal‐sch)Cl] ( 1 ), [Cu (sal‐tch)Cl] ( 2 ), [CH₂{Cu (sal‐sch)Cl}₂] ( 3 ) and [CH₂{Cu (sal‐tch)Cl}₂] ( 4 ) were isolated by reacting CuCl₂·2H₂O with [Hsal‐sch] ( I ), [Hsal‐tch] ( II ), [H₂bissal‐sch] ( III ) and [H₂bissal‐tch] ( IV ), respectively, in refluxing methanol. Complexes 1–4 have been covalently anchored in Merrifield resin through the amine nitrogen of the semicarbazide or thiosemicarbazide moiety. A number of analytical, spectroscopic and thermal techniques, such as CHNS analysis, Fourier transform‐infrared, UV–Vis, PMR, ¹³C‐NMR, electron paramagnetic resonance, scanning electron microscopy, energy‐dispersive X‐ray analysis, thermogravimetric analysis, atomic force microscopy, atomic absorption spectroscopy, and electrospray ionization‐mass spectrometry, were used to analyze and establish the molecular structure of the ligands ( I )–( IV ) and complexes ( 1 )–( 8 ) in solid state as well as in solution state. Grafted complexes 5 – 8 were employed as active catalysts for the oxidation of a series of alkenes in the presence of hydrogen peroxide. Copper hydroperoxo species ([Cu^III (sal‐sch)‐O‐O‐H]), which is believed to be the active intermediate, generated during the catalytic oxidation of alkenes, are identified. It was found that supported catalysts are very economical, green and efficient in contrast to their neat complexes as well as most of the recently reported heterogeneous catalysts.     

Synthesis,characterization, anti‐inflammatory and analgesic activity of transition metal complexes of 3‐[1‐(2‐hydroxyphenyl) ethylideamino]‐2‐phenyl‐3,4‐dihydroquinazolin‐4(3H)‐one

A new quinazolinone derivative, 3‐[1‐(2‐hydroxyphenyl)ethylideamino]‐2‐phenyl‐3,4‐dihydroquinazolin‐4(3H)‐one ( LH ) was synthesized by the condensation of 2‐hydroxyacetophenone‐2‐aminobenzoylhydrazone and benzaldehyde. The cyclization to form 1,2‐dihydroquinazolinone was confirmed by IR, 1D and 2D HETCOR studies. Coordination compounds of Co(II), Ni(II), Cu(II) and Zn(II) of LH were synthesized and characterized using various physico‐chemical studies like stoichiometric, conductivity, magnetic moment measurements and spectral techniques such as IR, NMR, UV‐vis and EPR spectroscopy. The elemental analysis and thermal studies suggested a general stoichiometry [M(HEPDQ)Cl] for all the complexes. A four‐coordinate geometry was assigned to all the complexes. The complexes along with the parent ligand were screened for their anti‐inflammatory activity, using carrageenan‐induced rat paw edema, and for their analgesic activity by Eddy's hot plate method. The activity of the ligand was enhanced on complexation with metal ions. This enhanced activity was attributed to the increased lipophilic nature of the complexes. Notable anti‐inflammatory activity was observed for Ni(II), Cu(II) and Zn(II) complexes. The analgesic activity of the ligand was greater than the standard at 60 min. and at a 10 mg kg⁻¹ dose, whereas the activity of Ni(II) and Cu(II) complexes at 10 mg kg⁻¹ dose was comparable with the standard used. Copyright © 2011 John Wiley & Sons, Ltd.     

Cryo‐XPS study of xanthate adsorption on pyrite

The adsorption of xanthate on pyrite has been extensively studied. However, the adsorption mechanisms remain a subject of controversy. Formation of both dixanthogen and metal‐xanthate complexes has been suggested. In this study, both room temperature X‐ray photoelectron spectroscopy (XPS) (RT‐XPS) and liquid nitrogen temperature XPS (Cryo‐XPS) were used to study interactions between pyrite and xanthate. While dixanthogen was not detected by RT‐XPS, it was successfully identified through C1s and S 2p peaks using Cryo‐XPS. The impact of pH and copper activation on adsorption of xanthate on pyrite was also investigated. It was found that at low pH, dixanthogen is the dominant species of xanthate adsorption on pyrite. At high pH, metal‐xanthate complexes were found to be prevalent on pyrite surfaces, which are responsible for the surface hydrophobicity. Copper activation showed a significant effect on xanthate adsorption on Cu‐activated pyrite, resulting in mostly the formation of Cu‐xanthate complexes rather than dixanthogen, mainly in the form of Cu(I)‐isopropyl xanthate complex (CuIPX). Copyright © 2012 John Wiley & Sons, Ltd.     

Diisopropyl fluorophosphate (DFP) degradation activity using transition metal–dipicolylamine complexes

Transition metal complexes have been extensively used as catalysts for organophosphorus agent decomposition to reduce their toxicity with their performance being strongly dependent on the nature of the metal ion. To investigate this dependence, we prepared dipicolylamine (DPA)‐containing complexes of Cu(II), Zn(II), Ni(II), Co(II), and Fe(II) and analyzed their activities for the degradation of diisopropyl fluorophosphate (DFP), a nerve agent surrogate compound. Cu(II)‐DPA complex showed fastest reaction kinetics while Zn(II)‐DPA and Ni(II)‐DPA exhibited more slower reactions. This observation can be explained using frontier molecular orbital (FMO) theory, which revealed that the nucleophilicity of the oxygen atom in water molecules in these transition metal complexes was well matched with reactivity order observed in experiments. These investigations combined with theoretical study provide valuable information for designing and predicting the activity of new transition metal–organic ligand complexes as a catalyst to decompose and reduce toxicity of organophosphorus nerve agents.     

Cu–N Dopants Boost Electron Transfer and Photooxidation Reactions of Carbon Dots

The broadband light‐absorption ability of carbon dots (CDs) has inspired their application in photocatalysis, however this has been impeded by poor electron transfer inside the CDs. Herein, we report the preparation of Cu–N‐doped CDs (Cu‐CDs) and investigate both the doping‐promoted electron transfer and the performance of the CDs in photooxidation reactions. The Cu–N doping was achieved through a one‐step pyrolytic synthesis of CDs with Na₂[Cu(EDTA)] as precursor. As confirmed by ESR, FTIR, and X‐ray photoelectron spectroscopies, the Cu species chelates with the carbon matrix through Cu–N complexes. As a result of the Cu–N doping, the electron‐accepting and ‐donating abilities were enhanced 2.5 and 1.5 times, and the electric conductivity was also increased to 171.8 μs cm^?1. As a result of these enhanced properties, the photocatalytic efficiency of CDs in the photooxidation reaction of 1,4‐dihydro‐2,6‐dimethylpyridine‐3,5‐dicarboxylate is improved 3.5‐fold after CD doping.     

Synthesis and Characterization of New Macrocyclic Cu（Ⅱ） Complexes from Various Diamines, Copper（Ⅱ） Nitrate and 1,4-Bis（2-formylphenoxy）butane

Six new macrocyclic complexes were synthesized by a template reaction of 1,4-bis（2-formylphenoxy）butane with diamines and Cu（NO3）2·3H2O and their structures were proposed on the basis of elemental analysis, FT-IR, UV-Vis, magnetic susceptibility measurements, molar conductivity measurements and mass spectra. The metal to ligand molar ratios of the Cu（Ⅱ） complexes were found to be 1 ： 1. The Cu（Ⅱ） complexes are 1 ： 2 electrolytes as shown by their molar conductivities （∧m） in DMF at 10^-3 mol·L^-1. Due to the existence of free ions the Cu（Ⅱ） complexes are electrically conductive. Their configurations were proposed to be probably distorted octahedral.